Barcelona were held to a 1-1 draw by Alaves at the Camp Nou on Saturday, with Sergi Barjuan overseeing his first match as interim coach.
An entertaining first half -- the first since Ronald Koeman was sacked midweek by the Catalans -- saw Barca probing early on and Alaves hitting on the counter-attack, but neither team found a way through and the teams went to the break tied 0-0.
A moment of individual brilliance from Memphis saw the hosts take the lead early in the second, as the Netherlands international cut onto his right foot and curled a lovely shot into the back of the net from distance.
The withdrawal of Aguero may be most concerning. Barca haven't confirmed what the problem was, but it appeared to be related to his chest and he was taken to hospital for further tests.
After defeats by Real Madrid and Rayo Vallecano which led to Koeman sacking, only 37,000 fans turned up at the Camp Nou to see the first game under caretaker coach Sergi Barjuan, the club's worst attendance for 20 years.
Eric Garcia had Barca's best opportunity in the first half with a header and Aguero's long-distance shot flew wide but the best chance fell to Alaves' Edgar Mendes.
Barcelona came out with more aggressive intent after the interval and Depay produced a stunning strike to register his fifth goal of the season.
Rioja responded quickly, however, running on to Joselu's backheel to round Ter Stegen and place the ball into an empty net.
Barcelona's 17-year-old midfielder Gavi dribbled past four Alaves defenders and set up Memphis whose effort hit the post and Nico also created a chance for the Dutchman which was saved by keeper Antonio Sivera.
The result leaves Barca stuck in ninth place on 16 points, while Alaves will cherish the point more as it keeps them narrowly outside the LaLiga relegation zone.
Information from Reuters was used in this report.